Golf Club and Golf Club Head with Stiffening Element

ABSTRACT

Golf club and golf club head structures include a ball striking face, a frame member and a perimeter stiffening element. The frame member may extend rearwardly from a perimeter of the ball striking face. The perimeter stiffening element may extend along at least a portion of the perimeter of the ball striking face and further may extend from the ball striking face to the frame member. The thickness of the ball striking face may be less than or equal to 2.0 mm. The cross-sectional area of the perimeter stiffening element may be greater than or equal to 10 mm 2 . The golf club head may be a wood-type club head.

FIELD OF THE INVENTION

Aspects of this invention relate generally to golf clubs and golf club heads. Particular example aspects relate to a golf club head having a ball striking surface with a stiffening feature.

BACKGROUND

Golf is enjoyed by a wide variety of players—players of different genders and dramatically different ages and/or skill levels. Golf is somewhat unique in the sporting world in that such diverse collections of players can play together in golf events, even in direct competition with one another (e.g., using handicapped scoring, different tee boxes, in team formats, etc.), and still enjoy the golf outing or competition. These factors, together with the increased availability of golf programming on television (e.g., golf tournaments, golf news, golf history, and/or other golf programming) and the rise of well known golf superstars, at least in part, have increased golf's popularity in recent years, both in the United States and across the world.

Golfers at all skill levels seek to improve their performance, lower their golf scores, and reach that next performance “level.” Manufacturers of all types of golf equipment have responded to these demands, and in recent years, the industry has witnessed dramatic changes and improvements in golf equipment. For example, a wide range of different golf ball models now are available, with balls designed to complement specific swing speeds and/or other player characteristics or preferences, e.g., with some balls designed to fly farther and/or straighter; some designed to provide higher or flatter trajectories; some designed to provide more spin, control, and/or feel (particularly around the greens); some designed for faster or slower swing speeds; etc. A host of swing and/or teaching aids also are available on the market that promise to help lower one's golf scores.

Being the sole instrument that sets a golf ball in motion during play, the golf club also has been the subject of much technological research and advancement in recent years. For example, the market has seen improvements in golf club heads, shafts, and grips in recent years. Additionally, other technological advancements have been made in an effort to better match the various elements of the golf club and characteristics of a golf ball to a particular user's swing features or characteristics (e.g., club fitting technology, ball launch angle measurement technology, etc.).

Because golf clubs typically are designed to contact the ball at or around the center of the face, off-center hits may result in less energy being transferred to the ball, thereby decreasing the distance of the shot. The energy or velocity transferred to the ball by a golf club also may be related, at least in part, to the flexibility of the club face at the point of contact, and can be expressed using a measurement called coefficient of restitution (“COR”). Accordingly, it would be advantageous to provide a golf club head having a flexible ball striking surface and other structural features that provide an improved or maximized COR. The present invention seeks to overcome certain of the limitations discussed above and other drawbacks of the prior art, and to provide features not heretofore available.

SUMMARY OF THE INVENTION

The following presents a simplified summary in order to provide a basic understanding of some aspects of the invention. The summary is not an extensive overview of the invention. It is neither intended to identify key or critical elements of the invention nor to delineate the scope of the invention. The following summary merely presents some concepts of the invention in a simplified form as a prelude to the description below.

A golf club and golf club head structures having a ball striking face, a frame member and a perimeter stiffening element are disclosed herein. The golf club head may be a wood-type club head. Further, the club head may have an interior cavity. The golf club head may have a volume greater than or equal to 440 cc and a ball striking face area greater than or equal to 32 cm²

According to certain aspects, the frame member may extend rearwardly from a perimeter of the ball striking face. The perimeter stiffening element may extend along at least a portion of the perimeter of the ball striking face and further may extend from the ball striking face to the frame member.

According to other aspects, a thickness of the perimeter stiffening element may be greater than or equal to a thickness of the ball striking face adjacent to the perimeter stiffening element. A width of the perimeter stiffening element may be greater than or equal to a thickness of the frame element adjacent to the perimeter stiffening element.

Further, the thickness of the ball striking face adjacent to the perimeter stiffening element may be greater than the thickness of the frame member adjacent to the perimeter stiffening element.

The coefficient of restitution of the club head may be greater than or equal to 0.830.

According to certain other aspects, the cross-sectional area of the perimeter stiffening element may be greater than or equal to 10 mm². Further, the thickness of the perimeter stiffening element may be greater than or equal to 4.0 mm and/or the width of the perimeter stiffening element may be greater than or equal to 3.0 mm. Even further, the out-of-plane bending stiffness (EI_(B)) of the perimeter stiffening element may range from 1500 in²-lb to 2500 in²-lb. The torsional stiffness (GJ) of the perimeter stiffening element may range from 1200 in²-lb to 1600 in²-lb.

The ratio of the thickness of the perimeter stiffening element to the width to the perimeter stiffening element may be greater than or equal to 1:1. The ratio of the thickness of the perimeter stiffening element to the thickness of the ball striking face adjacent to the perimeter stiffening element may range from approximately 2:1 to approximately 4:1. The thickness of the perimeter stiffening element may range from approximately 2.5 mm to approximately 7.5 mm. The width of the perimeter stiffening element may have a value that is within ±20% of the value of the thickness of the perimeter stiffening element.

The thickness of the frame member may be less than or equal to 1.0 mm. Optionally the thickness of the frame member adjacent to the perimeter stiffening element may range from approximately 0.25 mm to approximately 1.25 mm. According to some embodiments, the thickness of the ball striking face may be less than or equal to 2.0 mm. Alternatively, the thickness of the ball striking face adjacent to the perimeter stiffening element may range from approximately 0.5 mm to approximately 2.5 mm. The ratio of the thickness of the ball striking face adjacent to the perimeter stiffening element to the thickness of the frame member adjacent to the perimeter stiffening element may be greater than or equal to approximately 1.5:1.

According to some aspects, the perimeter stiffening element may be integrally joined to the frame member. Further, the perimeter stiffening element may be integrally joined to the ball striking face. According to certain embodiments, the ball striking face, the frame member and the perimeter stiffening element may be unitarily formed. Further, the ball striking face, the frame member and the perimeter stiffening element may be formed of a titanium material.

According to some aspects, a golf club and golf club head structures have a ball striking face, a frame member and a perimeter stiffening element. The ball striking face may be configured to flex inward upon contacting a golf ball. The frame member may extend around and be integrally joined to the ball striking face. The perimeter stiffening element may extend around at least majority of a perimeter of the ball striking face. Further, the perimeter stiffening element may be joined to an interior surface of the ball striking face and to an interior surface of the frame member. The ball striking face may have a thickness, measured adjacent to the perimeter stiffening element, which ranges from approximately 1.25 mm to approximately 2.5 mm. The frame member may have a thickness, measured adjacent to the perimeter stiffening element, which ranges from approximately 0.40 mm to approximately 1.0 mm. The perimeter stiffening element may have a cross-sectional area greater than or equal to 20 mm². The coefficient of restitution of the club head may be greater than or equal to 0.830.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and not limited in the accompanying figures, in which like reference numerals indicate similar elements throughout, and in which:

FIG. 1 is a top plan view of a golf club head that schematically illustrates features according to certain aspects of this invention.

FIG. 2 is a front elevation view of a golf club incorporating the golf club head of FIG. 1.

FIG. 3 is side perspective view of the golf club head of FIG. 1, viewed generally from a toe side of the golf club head.

FIG. 4 is rear perspective view of the golf club head of FIG. 1.

FIG. 5 is side perspective view of the golf club head of FIG. 1, viewed generally from a heel side of the club head.

FIG. 6 is bottom perspective view of the golf club head of FIG. 1.

FIG. 7 is a cross-sectional view taken along line VII-VII of the golf club head of FIG. 1 further illustrating the ball striking face, the frame member and a perimeter stiffening element according to certain aspects of the invention.

FIG. 7A is an enlarged view of a portion of the golf club head shown in FIG. 7.

FIG. 8 is a cross-sectional view taken along line VIII-VIII of the golf club head of FIG. 1 further illustrating the perimeter stiffening element of FIG. 7 according to certain aspects of the invention.

FIG. 9 is a snapshot of results of a computer analysis of a simplified, axisymmetric model of a comparative face/frame example.

FIG. 10 is a snapshot of results of a computer analysis of a simplified, axisymmetric model of a face/frame example which further includes a perimeter stiffening element.

FIGS. 11A through 11D are cross-sectional views of a portion of a golf club head illustrating exemplary configurations of perimeter stiffening elements according to various aspects of the invention.

FIG. 12 is a cross-sectional view, similar to the cross-sectional view of FIG. 7, of a golf club head further illustrating a perimeter stiffening element according to certain additional aspects of the invention.

FIG. 13 is a cross-sectional view, similar to the cross-sectional view of FIG. 7, of a golf club head further illustrating a perimeter stiffening element according to even other additional aspects of the invention.

The reader is advised that the various parts shown in these drawings are not necessarily drawn to scale.

DETAILED DESCRIPTION

The following description and the accompanying figures disclose features of golf clubs and golf club head structures in accordance with examples of the present invention.

I. GENERAL DESCRIPTION OF EXAMPLE GOLF CLUBS AND GOLF CLUB HEADS IN ACCORDANCE WITH THIS INVENTION

When a player hits a golf ball, both the golf ball and the golf club head (particularly, the ball striking face) deform—the golf ball compressing in diameter against the ball striking face and the ball striking face flexing inward. Because the ball is of a more resilient material and its mass is so much smaller than the ball striking face of the club head, the golf ball causes a greater energy loss than the amount that the face of the head may lose when its face flexes inward—in fact, the golf ball may be responsible for up to 80% of the loss of energy between the two. As a result, if the ball striking face can be designed so that the face deflects more, the golf ball will compress less, resulting in a greater ball speed velocity in relation to the player's swing speed.

The development of thinner ball striking faces leads to a more flexible face, thereby reducing the energy loss associated with deformation of the golf ball. A limit case of this concept would be analogous to a trampoline, which consists of a thin membrane, supported by springs and a frame. However, if the frame of the trampoline is too flexible, both control and speed of the rebounding ball can be lost.

For flexible ball striking faces, it was determined that adding a stiffening ring around the perimeter (i.e., where the ball striking face meets the front frame of the club head) improves the overall response and increases the COR. Modeling and analyses have shown that this stiffening ring isolates the club head energy at the ball striking face, where it is best poised to return more energy to the ball during the rebound process. Thus, less energy flows beyond the ball striking face, such that, for example, outward deformations of the front frame of the club head adjacent to the ball striking face are reduced and tend to be more localized. Additionally, analyses show that peak deformations of the ball striking face with the stiffening ring occur earlier during the impact time than of the ball striking face without a stiffening ring. It is expected that the combination of these factors would allow the club head having the stiffening ring around the perimeter of the balls striking face to return more energy to the ball, rather than dissipating it through club head front frame vibrations. With more energy being returned to the ball, a significant increase in COR is expected to be produced.

These findings may be applied to any of various golf club heads and various types of golf clubs in accordance with aspects described herein. For instance, a perimeter stiffening element may be used with wood-type golf clubs and golf club heads, e.g., clubs and club heads typically used for drivers and fairway woods, as well as for “wood-type” utility or hybrid clubs, or the like. Such club head structures may have little or no actual “wood” material and still may be referred to conventionally in the art as “woods” (e.g., “metal woods,” “fairway woods,” etc.). Further, a perimeter stiffening element may also be used with iron-type, hybrid-type, utility type, etc. golf clubs and golf club head structures.

In accordance with the above, aspects of this invention relate to golf club and golf club head structures. In some examples, a golf club head may include a golf club head body having a crown, a sole, a toe, a heel, a rear and a ball striking face. The crown, sole, toe, heel, rear and ball striking face may define an at least substantially enclosed interior portion of the golf club head. The portion of the club head that extends rearwardly from the ball striking face may be referred to as a frame member.

The golf club and golf club head includes a perimeter stiffening element extending around the inside perimeter edge of the ball striking face. The perimeter stiffening element couples the ball striking face to the frame member. The perimeter stiffening element may extend along just a portion of the perimeter of the ball striking face or it may extend completely around the perimeter of the ball striking face. The perimeter stiffening element may be continuous or discontinuous. Further, the perimeter stiffening element may have a constant cross-sectional area and/or shape or the area and/or the shape may vary as the perimeter stiffening element extends around the perimeter of the ball striking face. Additionally, the perimeter stiffening element may be integrally formed with the ball striking face and/or with the frame member (or portions thereof). Alternatively, the perimeter stiffening element may be formed separately from the ball striking face and/or the frame member and joined to the ball striking face and/or the frame member in a secondary or subsequent operation. The perimeter stiffening element may be formed of the same or different material(s) than the ball striking face and/or the frame member.

According to certain aspect, the thickness of the perimeter stiffening element may be greater than or equal to a thickness of the ball striking face adjacent to the perimeter stiffening element, and the width of the perimeter stiffening element may be greater than or equal to a thickness of the frame element adjacent to the perimeter stiffening element. For example, the thickness of the perimeter stiffening element may be greater than one-and-a-half times the thickness of the ball striking face or greater than twice the thickness of the ball striking face. The width of the perimeter stiffening element may be greater than twice the thickness of the frame element, or even greater than triple the thickness of the frame element.

According to some aspects, the thickness of the perimeter stiffening element may be greater than or equal to the width of the perimeter stiffening element.

Further, the thickness of the ball striking face adjacent to the perimeter stiffening element may be greater than the thickness of the frame member adjacent to the perimeter stiffening element.

Given the general description of various example aspects of the invention provided above, more detailed descriptions of various specific examples of golf clubs and golf club head structures according to the invention are provided below.

II. DETAILED DESCRIPTION OF EXAMPLE GOLF CLUBS AND GOLF CLUB HEADS

The following discussion and accompanying figures describe various example golf clubs and golf club head structures in accordance with various aspects of the present invention. When the same reference number appears in more than one drawing, that reference number is used consistently in this specification and the drawings to refer to the same or similar parts throughout.

“Integrally joined” refers to a single piece, component, element, member, etc. that cannot be separated into multiple pieces or subcomponents without structural damage. Integrally joining techniques including unitarily forming the piece or component (i.e., manufacturing the piece as a single unit from the raw materials used to form the piece), and further includes irreversibly or permanently joining (such as adhesively joining, cementing, welding, brazing, soldering, or the like) originally separate pieces so that the pieces effectively become inseparable without structural damage.

“Transverse” means extending across or in a cross direction to a line, plane, edge, surface, etc., defined at an actual or virtual intersection point, but does not necessarily imply a perpendicular intersection.

Specific examples and features of golf club heads and golf club structures will be described in detail below in conjunction with the example golf club structures illustrated in FIGS. 1 through 8. The specific shape and design of the club head 14 may be at least partially dictated by the intended use of the club. For example, in the club 10 shown in FIGS. 1-8, the head 14 has a relatively large volume, as the club 10 is designed for use as a driver or wood-type club and is intended to hit the ball accurately over long distances. When configured as a wood-type club, the club head 14 may have a volume of at least 400 cc, and in some structures, at least 440 cc, or even at least 460 cc. According to another aspect, when configured as a wood-type club, the club head 14 may have a relatively large ball striking face surface area. By way of non-limiting example, the area of the ball striking face may be greater than or equal to 4.7 square inches (approximately 30 cm²), greater than or equal to 5.0 square inches (approximately 32 cm²), or even greater than or equal to 5.2 square inches (approximately 33.5 cm²). In other applications, such as for a different type of golf club, the head may be designed to have different configurations and/or dimension as may be readily determined by those skilled in the art. Thus, the club head 14 may be any of various types of golf club heads and may be constructed in any suitable manner and/or from any suitable material, including from conventional materials and/or in conventional manners known and used in the art.

FIGS. 1-8 generally illustrate an example wood-type golf club 10 and/or golf club head 14 according to certain aspects. Referring to FIG. 2, a golf club shaft 12 may be received in, engaged with, and/or attached to the golf club head 14 in any desired manner, including in various adjustable manners which permit movement of the shaft 12 with respect to the golf club head 14. Any attachment method and/or structure as are known and used in the art also may be used without departing from this invention. For example, a socket 16 or other shaft receiving element as shown in FIG. 1-8 may be provided. Any desired hosel, socket and/or head/shaft interconnection structure may be used without departing from this invention, including conventional hosel and/or head/shaft interconnection structures as are known and used in the art. The shaft 12 may be made from any suitable materials, including conventional materials known and used in the art, such as graphite based materials, composite or other non-metal materials, steel materials (including stainless steel), aluminum materials, other metal alloy materials, polymeric materials, combinations of various materials, and the like.

Additionally, a grip or handle (not shown) may be provided on a proximal end of the shaft 12. Any suitable grip material may be used without departing from this invention, including, by way of non-limiting examples: elastomeric materials, leather materials, rubber or other materials including cord or other fabric material embedded therein, polymeric materials, and the like. The grip may be secured to the shaft 12 in any suitable manner, including in conventional manners known and used in the art, e.g., using adhesives or cements; using welding, soldering, brazing or the like; using mechanical connectors (such as threads, retaining elements, etc.); etc. As another example, the grip may be integrally formed as a unitary, one-piece construction with the shaft 12.

In the example structure shown in FIGS. 1-8, the club head 14 includes a number of different regions, such as a ball striking face 17, crown 18, a sole 28, a heel 24, a toe 20, a rear 22 and a hosel region 26. As noted above, a wide variety of overall club head constructions are possible without departing from this invention. By way of non-limiting examples, some or all of the various individual parts of the club head 14 described above may be made from multiple pieces that are connected and/or joined together (e.g., by welding or other fusing techniques; by adhesives; by mechanical connectors; etc.). The various club components may be permanently and integrally joined or may be joined such that disassembly is possible. The various parts (e.g., ball striking face, 17, crown 18, sole 28, etc.) may be made from any suitable material and/or combinations of different materials, including materials that are conventionally known and used in the art, such as metal materials, including lightweight metal materials. More specific examples of suitable lightweight metal materials include steel, titanium and titanium alloys, aluminum and aluminum alloys, magnesium and magnesium alloys, etc.

As additional examples or alternatives, in order to reduce the weight of the club head 14, one or more portions of the club head 14 may be made from a composite material, such as from carbon fiber composite materials that are conventionally known and used in the art. Other suitable composite materials that may be used for one or more portions of the club head 14 include, for example: fiberglass composite materials, aramid fiber reinforced composite materials, basalt fiber reinforced composite materials, polymer materials, ceramic materials, etc. The composite material(s) may be incorporated as part of the club head 14 in any suitable manner, including in conventional manners that are known and used in the art.

In the embodiment of FIGS. 1-8 and particularly referring to FIG. 7, the club head 14 may define an enclosed (or substantially enclosed) inner cavity 21. In one embodiment, the inner cavity 21 may be hollow, e.g., essentially filled with air. However, in other embodiments, the head 14 could be filled with another material, such as foam. In still further embodiments, the solid materials of the head may occupy a greater proportion of the volume, and the head may have a smaller cavity or no inner cavity at all. It is understood that the inner cavity may not be completely enclosed in some embodiments.

The ball striking face 17 is located at the front of the club head 14, and has a ball striking surface 17 b located thereon and an inner surface 17 c opposite the ball striking surface 17 b, as best illustrated in FIGS. 7 and 8. The ball striking face 17 is adapted to deflect rearwardly when it strikes a golf ball. Additionally, the ball striking face 17 defines a perimeter 17 d. With the club in an address position, the perimeter 17 d may be defined as the edge of the ball striking face 17 wherein the club head transitions from having a generally vertical, forward facing surface (i.e., the surface of the ball striking face 17) to a generally vertical, side facing surface (i.e., the surfaces of the toe 20 and/or the heel 24) and/or to a generally horizontal surface (i.e., the surfaces of the crown 18 and/or the sole 28). For purposes of this disclosure, the area within the perimeter 17 d may define the area of the ball striking face 17.

The ball striking face 17 may be formed from a single piece of material. For example, the ball striking face 17 may be formed of a metal material, such as a titanium alloy (e.g., Ti-6Al-4V). Other high strength materials, such as stainless steel or other steel alloys may be used. Additionally, vitreous alloys such as iron-boron, nickel-copper, nickel-zirconium, nickel-phosphorous, and the like may be used. Further, the ball striking face 17 may be formed from ceramics, composites and/or other metal. Even further, the striking face may be formed from amorphous metals, including alloys containing zirconium, titanium, beryllium, niobium, copper, nickel, etc., using a bulk-solidifying process. Such bulk-solidifying amorphous metals are disclosed, for example, in U.S. Pat. No. 7,357,731, issued Apr. 15, 2008, to Johnson et al., and hereby incorporated by reference in its entirety.

The ball striking face 17 may be forged, drawn, cast, machined, injection bmolded, powder-metal formed, milled, etched, etc. Alternatively, the ball striking face 17 may be formed from multiple pieces of material that are subsequently joined together.

Referring to FIGS. 1 and 2, the ball striking surface 17 b is a region or surface that may be essentially flat or that may have a slight curvature or bow (also known as “bulge” when referring to horizontal curvature or “roll” when referring to vertical curvature). Although the golf ball may contact the ball striking surface 17 b at any spot on the face, the desired-point-of-contact 17 a of the ball striking surface 17 b with the golf ball is typically approximately centered within the ball striking surface 17 b. Typically, the ball striking surface 17 b may have a plurality of score lines formed thereon.

Further, the ball striking face 17 may generally be provided with a loft angle, such that at the point of impact (and also at the address position, i.e., when the club head is positioned on the ground adjacent to the golf ball prior to the initiation of the backswing) the ball striking surface 17 b is not perpendicular to the ground. Generally, the loft angle is meant to affect the initial upward trajectory of the golf ball—increased loft induces greater ball trajectory heights. Standard loft for a driver is around 10 degrees, although lofts may frequently range from 7 or 8 degrees up to 14 degrees.

Even further, the ball striking face 17 may be provided with a face angle, such that at the point of impact the ball striking surface 17 b is not parallel to the orientation of the shaft. Generally, the face angle is meant to counteract a particular golfer's tendency to hook or slice his shots—an “open face” is meant to counteract a tendency to hook; a “closed face” is meant to counteract a tendency to slice.

Although, bulge and roll and face and loft angles have been described above with respect to the ball striking face 17 and the ball striking surface 17 b, generally, the ball striking face 17 may be considered to be a relatively flat, planar component. Referring to FIGS. 7 and 7A, the ball striking face 17 may be formed as a thin-walled titanium-alloy plate. In certain embodiments, a titanium-alloy thin-walled ball striking face 17 may have a constant thickness (t₁) of approximately 0.075 inches (approximately 1.9 mm). In other embodiments, a titanium-alloy thin-walled ball striking face 17 may have a constant thickness (t₁) of approximately 0.083 inches (approximately 2.1 mm). Optionally, the ball striking face 17 may have a constant thickness t₁ ranging from 0.050 inches (approximately 1.25 mm) to 0.120 inches (approximately 3.05 mm), ranging from 0.060 inches (approximately 1.50 mm) to 0.120 inches (approximately 3.05 mm), or even ranging from 0.060 inches (approximately 1.5 mm) to 0.080 inches (approximately 2.0 mm). According to other aspects, the thickness t₁ of the ball striking face 17 may vary. By way of non-limiting example, the thin-walled plate may be thicker at the desired-point of contact 17 a and thinner at or near its perimeter 17 d. As a specific example, the thickness t₁ of the ball striking face 17 at the desired-point-of-contact 17 a may range from 0.083 inches (approximately 2.1 mm) to 0.138 inches (approximately 3.50 mm) and the thickness at or near its perimeter 17 d may range from 0.050 inches (approximately 1.25 mm) to 0.080 inches (approximately 2.03 mm) or from 0.060 inches (approximately 1.50 mm) to 0.098 inches (approximately 2.50 mm).

According to certain aspects, the club head 14 may include a front body portion 14 a and an aft body portion 14 b. In certain embodiments, the two portions 14 a, 14 b may actually be two components that are formed separately and then subsequently assembled to form the club head. Thus, for example as shown in FIGS. 1-8, front body portion 14 a and aft body portion 14 b are assembled to form club head 14. Optionally, a gasket (not shown) may be included between the front body portion 14 a and the aft body portion 14 b.

The front body portion 14 a may include the ball striking face 17, extending generally within a plane, with a frame member 19, extending generally transversely to the plane of the ball striking face 17 and rearwardly from the perimeter 17 d of the ball striking face 17. The perimeter 17 d may define the intersection of the ball striking face 17 with the frame member 19. The frame member 19 may extend continuously around the perimeter 17 d of the ball striking face 17.

Further, the frame member 19 may include and/or form portions of the crown 18, the toe 20, the sole 28, the heel 24 and/or the hosel region 26. In some embodiments, the frame member 19 may integrally and/or unitarily formed with the crown 18, the toe 20, the sole 28, the heel 24 and/or the hosel region 26. Thus, the frame member 19 is that portion of the club head that lies adjacent to and frames and extends around the ball striking face 17. In those embodiments wherein the frame member 19 may be separately formed and/or distinguishable from the more aftward portions of the club head, the rearward extent of the frame member 19 may be relatively constant, such as shown in FIGS. 7 and 7A. In other words, the breadth dimension (i.e., the front-to-back dimension) of the frame member 19 may be relatively constant. Alternatively, the rearward extent of the frame member 19 may vary as the frame member 19 extends around the perimeter 17 d of the ball striking face 17. For example, the frame member 19 may extend rearwardly into the crown 18 and into the sole 28 more than into the toe 20 or into the heel 24. Even further, if desired, the socket 16 and/or a portion of the hosel region 26 may be unitarily formed with or integrally joined to the frame member 19 as part of the front body portion 14 a.

According to some aspects, the frame member 19 may have a wall thickness t₂ that is less than the thickness t₁ of the ball striking face 17. Thus, for example, the thickness t₂ of the frame member 19 may be constant and may be approximately 0.025 inches (approximately 0.635 mm). Optionally, the thickness t₂ of the frame member 19 may range from 0.010 inches (approximately 0.25 mm) to 0.075 inches (approximately 1.91 mm), ranging from 0.010 inches (approximately 0.25 mm) to 0.050 inches (approximately 1.25 mm), ranging from 0.020 inches (approximately 0.508 mm) to 0.050 inches (approximately 1.25 mm), or even ranging from 0.015 inches (approximately 0.40 mm) to 0.035 inches (approximately 0.90 mm). According to other aspects, the thickness t₂ of the frame member 19 may vary. Thus, for example, the frame member 19 may be thicker in the sole region than in the crown region. As another example, the frame member 19 may be thickest closest to the ball striking face 17 and thinner as it extends rearwardly away from the face 17. Further, by way of non-limiting example, the frame member 19 may be considered to be a thin-walled shell structure, i.e., a structure that generally reacts loads by developing in-plane stresses.

According to certain aspects, a ratio of the thickness t₁ of the ball striking face 17 to the thickness t₂ of the frame member 19 may be greater than approximately 1.5:1, greater than approximately 2.5:1, greater than approximately 3:1, greater than approximately 4:1, even greater than approximately 5:1, or even up to approximately 6:1. Thus, for example, if the thickness t₁ of the ball striking face 17 is 0.075 inches (approximately 1.905 mm) and the thickness t₂ of the frame member 19 is 0.025 inches (approximately 0.635 mm), the ratio is approximately 3:1. If the thickness t₁ of the ball striking face 17 varies and/or if the thickness t₂ of the frame member 19 varies, the ratio may be determined using the minimum thicknesses t₁, t₂.

Referring to FIGS. 7, 7A and 8, the front body portion 14 a may further include a perimeter stiffening element 117. FIG. 7 is a schematic cross-sectional view of the golf club head 14 of FIGS. 1-6 taken along line VII-VII of FIG. 1. The club head 14 may include other elements, structural or non-structural, not shown in the schematic of FIG. 7. FIG. 7A is an enlarged view of a portion of FIG. 7. FIG. 8 is a schematic cross-sectional view of the golf club head 14 of FIGS. 1-6 taken along line VIII-VIII of FIG. 1.

The perimeter stiffening element 117 is located where the frame member 19 joins the ball striking face 17. Specifically, the perimeter stiffening element 117 is located on the interior surface of the ball striking face 17 and extends along the perimeter of the ball striking face 17. According to certain aspects, the perimeter stiffening element 117 may extend completely around the perimeter 17 d of the ball striking face 17. The perimeter stiffening element 117 is also located on the interior surface of the frame member 19. In other words, the perimeter stiffening element 117 extends from the ball striking face 17 to the frame member 19, further reinforcing the attachment of the frame member to the ball striking face 17.

The perimeter stiffening element 117 stiffens the ball striking face 17 and also stiffens the frame member 19. Further, the perimeter stiffening element 117 stiffens the attachment of the ball striking face 17 to the frame member 19, such that the frame member 19 and the ball striking face 17 are more strongly coupled to each other. Thus, deflections and stresses of the ball striking face 17 and of the frame member 19 are decreased in the vicinity of their intersection.

As noted above, if the ball striking face 17 has a very thin thickness t₁, a high COR response due to a trampoline-like effect may result upon impact with a golf ball. However, as also noted above, if the perimeter of the ball striking face 17 is too flexible, control over the rebounding golf ball may be reduced. The presence of the perimeter stiffening element 117 may allow the ball striking face 17 to be made of a thin or relatively thinner material than would be possible for club heads without a perimeter stiffening element 117, and thus may allow for more flexibility of the ball striking face 17 and ultimately a higher COR, with greater control over the rebounding golf ball. Additionally, the perimeter stiffening element 117 may aid in preventing over flexing of the ball striking face 17 and/or of the frame member 19. Over flexing could result in failure of the ball striking face 17 and/or of the frame member 19 (e.g., breaking, cracking, stress fatigue, etc.).

FIGS. 7, 7A and 8 illustrate an example embodiment of a perimeter stiffening element 117 that may be used to provide the above-described advantages. In FIG. 8, perimeter stiffening element 117 is shown extending around the perimeter 17 d of the ball striking face 17. As shown in FIGS. 7 and 7A, the perimeter stiffening element 117 extends from the interior, rear wall or surface of the ball striking face 17 to the interior, side wall or surface of the frame member 19. As shown in FIG. 7, the perimeter stiffening element 117 is nestled into the interior angle formed by the intersection (at perimeter 17 d) of the ball striking face 17 with the frame member 19. As such, the perimeter stiffening element 117 reinforces and stiffens this intersection. As shown in this particular embodiment, the perimeter stiffening element 117 may be unitarily formed with and/or integrally joined to the ball striking face 17. Further, the perimeter stiffening element 117 may be unitarily formed with and/or integrally joined to the frame member 19. Suitable methods for attaching the perimeter stiffening element 117 to the ball striking face 17 and/or to the frame member 19 may include welding, brazing, soldering, cementing, adhesives, co-molding, mechanically fastening, press and/or interference fitting, etc. The perimeter stiffening element 117 may be continuously attached to the ball striking face 17 and/or to the frame member 19 or may be attached discontinuously (e.g., spot attachment).

Referring to FIG. 7A, the perimeter stiffening element 117 has a front-to-back thickness t₃. The thickness t₃ of the perimeter stiffening element 117 is measured parallel to the thickness of the ball striking face 17. Further, the thickness t₃ of the perimeter stiffening element 117 is measured at the maximum thickness dimension for any given cross-section of the perimeter stiffening element 117. The thickness t₃ of the perimeter stiffening element 117 may be constant or it may vary along the perimeter of the ball striking face 17. Thus, the perimeter stiffening element 117 may, for example, be thicker along the crown perimeter edge and thinner along the toe perimeter edge. According to certain aspects, the thickness t₃ may be approximately equal to 5.0 mm (approximately 0.20 inches). By way of non-limiting examples, the thickness t₃ of the perimeter stiffening element 117 may be greater than or equal to 1.0 mm, greater than or equal to 2.0 mm, greater than or equal to 3.0 mm greater, than or equal to 4.0 mm, or even greater than or equal to 5.0 mm. According to other aspects, the thickness t₃ of the perimeter stiffening element 117 may lie between a lower and an upper limit. Thus, as a non-limiting example, the thickness t₃ of the perimeter stiffening element 117 may be greater than or equal to 1.0 mm and less than or equal to 6.0 mm. Alternatively, the thickness t₃ of the perimeter stiffening element 117 may be greater than or equal to 1.0 mm and less than or equal to 5.0 mm, greater than or equal to 2.0 mm and less than or equal to 6.0 mm, or even greater than or equal to 2.0 mm and less than or equal to 5.0 mm.

According to other aspects, the thickness t₃ of the perimeter stiffening element 117 may be related to the thickness t₁ of the ball striking face 17. For example, the thickness t₃ of the perimeter stiffening element 117 may be greater than or equal to the thickness t₁ of the ball striking face 17. By way of non-limiting example, the thickness t₃ of the perimeter stiffening element 117 may be greater than or equal to twice the thickness t₁ of the ball striking face 17. Optionally, the ratio of the thickness t₃ of the perimeter stiffening element 117 to the thickness t₁ of the ball striking face 17 may be greater than or equal to 3:1, or even greater than or equal to 4:1. Alternatively, it may be desirable to limit the thickness t₃ of the perimeter stiffening element 117 to between two and four times the thickness t₁ of the ball striking face 17 or even to between one and three times the thickness t₁ of the ball striking face 17.

Still referring to FIG. 7A, the perimeter stiffening element 117 has a width w₃. The width w₃ of the perimeter stiffening element 117 is measured parallel to the thickness t₂ of the frame member 19. Further, the width w₃ of the perimeter stiffening element 117 is measured at the maximum width dimension for any given cross-section of the perimeter stiffening element 117. The width w₃ of the perimeter stiffening element 117 may be constant or it may vary as the perimeter stiffening element 117 extends around the perimeter 17 c. According to certain aspects, the width w₃ may be approximately equal to 5.0 mm (approximately 0.20 inches). By way of non-limiting examples, the width w₃ of the perimeter stiffening element 117 may be greater than or equal to 1.0 mm, greater than or equal to 2.0 mm, greater than or equal to 3.0 mm greater, than or equal to 4.0 mm, or even greater than or equal to 5.0 mm. According to other aspects, the width w₃ of the perimeter stiffening element 117 may lie between a lower and an upper limit. Thus, as a non-limiting example, the width w₃ of the perimeter stiffening element 117 may be greater than or equal to 1.0 mm and less than or equal to 6.0 mm. Alternatively, the width w₃ of the perimeter stiffening element 117 may be greater than or equal to 1.0 mm and less than or equal to 5.0 mm, greater than or equal to 2.0 mm and less than or equal to 6.0 mm, or even greater than or equal to 2.0 mm and less than or equal to 5.0 mm.

According to certain aspects, the width w₃ of the perimeter stiffening element 117 may be related to the thickness t₃ of the perimeter stiffening element 117. For example, the ratio of the width w₃ of the perimeter stiffening element 117 to the thickness t₃ of the perimeter stiffening element 117 may be approximately 1:1. By way of other non-limiting examples, the width w₃ of the perimeter stiffening element 117 may be greater than the thickness t₃ of the perimeter stiffening element 117; greater than or equal to twice or even thrice the thickness t₃ of the perimeter stiffening element 117. On the other hand, it may be desirable to have the thickness t₃ of the perimeter stiffening element 117 greater than the width w₃ of the perimeter stiffening element 117. Thus, the ratio of the thickness t₃ of the perimeter stiffening element 117 to the width w₃ of the perimeter stiffening element 117 may be greater than 1:1; greater than 1.5:1, greater than 2:1, or even greater than 3:1.

According to other aspects, the width w₃ of the perimeter stiffening element 117 may be related to the thickness t₂ of the frame member 19. For example, the width w₃ of the perimeter stiffening element 117 may be greater than or equal to the thickness t₂ of the frame member 19. By way of non-limiting examples, the width w₃ of the perimeter stiffening element 117 may be greater than or equal to the twice or even thrice the thickness t₂ of the frame member 19. Further, it may be desirable to provide a perimeter stiffening element 117 having a width w₃ that is greater than or equal to four times, six times, eight times or even ten times the thickness t₂ of the frame member 19. Alternatively, the width w₃ of the perimeter stiffening element 117 may lie between four and ten times the thickness t₂ of the frame member 19 or even to between five and eight times the thickness t₂ of the frame member 19.

According to other aspects, the perimeter stiffening element 117 may have a cross-sectional area (A) that is approximately 26 mm² (approximately 0.04 square inches). When determining the cross-sectional area A of the perimeter stiffening element 117 the areas due to the thicknesses t₁ and t₂ of the ball striking face 17 and the frame member 19, respectively, would typically not be included in the calculation. By way of non-limiting example, the perimeter stiffening element 117 may have a cross-sectional area A that ranges from approximately 5 mm² to approximately 35 mm², from approximately 10 mm² to approximately 30 mm², from approximately 15 mm² to approximately 25 mm², or even from approximately 15 mm² to approximately 20 mm². It is expected that, generally, the greater the cross-sectional area, the stiffer the perimeter stiffening element will be, and the greater the isolation of the dynamic response of the ball striking face 17 from the dynamic response of the frame member 19. Thus, by way of other non-limiting examples, the perimeter stiffening element 117 may have a cross-sectional area A that is greater than approximately 5 mm², greater than approximately 10 mm², greater than approximately 15 mm², greater than approximately 20 mm², or even greater than approximately 25 mm².

A simplified, axisymmetric analytical model developed with an LS-DYNA transient finite element analysis program was developed to investigate various potential high ball speed design concepts. FIGS. 9 and 10 show the results of two of these finite element computer analyses of a section of a front body portion 14 a. The analytical model of FIG. 9 does not include a perimeter stiffening element. The analytical model of FIG. 10 does include a perimeter stiffening element. Using these models, the bounce velocity of a ball impacting a static specimen was computationally determined and used to calculate a coefficient of restitution (COR) for comparative purposes. Further, deflections and stresses were computationally determined and used for comparative purposes.

As a baseline, an analytical model similar to that shown in FIG. 9 (no perimeter stiffening element) was supplied with thickness dimensions for the ball striking face 17 and the frame member 19 that are typical of modern driver heads (t₁=0.115 inches (approximately 2.92 mm); t₂=0.060 inches (approximately 1.52 mm)). This baseline is reported as Run No. 1. The analytical coefficient of restitution (COR) for this design is 0.852, as noted in Table I.

FIG. 9 and Run No. 2 of Table I illustrate the computer modeling results of the potential flex of the ball striking face 17 and the frame member 19, still without the presence of a perimeter stiffening element 117, but with the dimensions of the model reduced. For Run No. 2, the ball striking face thickness t₁ was reduced to 0.075 inches (approximately 1.905 mm) and the frame member thickness t₂ was reduced to 0.025 inches (approximately 0.635 mm). This resulted in an increase in the analytical COR to 0.858 (see Table I). However, as shown on FIG. 9, the frame member 19 was significantly deformed in the outward (radial) direction under this impact. In other words, the fairly significant reduction in the ball striking face thickness t₁ (from 0.115 inches/2.92 mm to 0.075 inches/1.905 mm), when paired with a reduction in the frame member thickness t₂ (from 0.060 inches/1.52 mm to 0.025 inches/0.635 mm), produces only a minor increase in ball speed, yet at the same time results in the frame member 19 experiencing significant, detrimental deformations. It was concluded that, for this design, the perimeter of the thin ball striking face 17 was overly flexible.

FIG. 10 and Run No. 3 of Table I illustrate the computer modeling results of the potential flex of the ball striking surface 17 and the frame the potential member 19 with the presence of the perimeter stiffening element 117. For Run No. 3, the ball striking face thickness t₁ was maintained at 0.075 inches (approximately 1.905 mm) and the frame member thickness t₂ was maintained at 0.025 inches (approximately 0.635 mm). However, for this run, an analytical perimeter stiffening element, as best shown in FIG. 10, was added to the model. The perimeter stiffening element had a thickness t₃=0.20 inches (approximately 5.08 mm), a width w₃=0.20 inches (approximately 5.08 mm), and a cross-sectional area A=0.004 in² (approximately 25.8 mm). This resulted in a very significant increase in the analytical COR to 0.883 (see Table I). It was considered that by adding the perimeter stiffening element 117, the overall response would be more typical of a high COR trampoline, in that the perimeter stiffening element 117 would isolate the club head energy at the face, where it is best poised to return more energy to the ball during the rebound process.

TABLE I Analytical COR Comparison Run Dimensions COR # 1 t₁ = 0.115 inches (~2.92 mm) 0.852 t₂ = 0.060 inches (~1.52 mm) no perimeter stiffening element # 2 t₁ = 0.075 inches (~1.905 mm) 0.858 t₂ = 0.025 inches (~0.635 mm) no perimeter stiffening element # 3 t₁ = 0.075 inches (~1.905 mm) 0.883 t₂ = 0.025 inches (~0.635 mm) perimeter stiffening element: t₃ = 0.20 inches (~5.08 mm) W₃ = 0.20 inches (~5.08 mm) A = 0.004 in² (~25.8 mm²)

Further, as seen by comparing FIG. 9 with FIG. 10, the outward (radial) deformation of the frame member 19 is reduced by the presence of the perimeter stiffening element 117. The “mx” and “mn” symbols show the locations of the maximum and minimum deflection points. In FIG. 9, the mn (smallest vertical deflection) is at the front, outer diameter of the face (−0.008 inches). As shown in FIG. 10, with the perimeter stiffening element 117 added the displacement of that location decreases to −0.003 inches. Even further, with the addition of the perimeter stiffening element 117, the deformations of the ball striking surface 17 also tend to be more local to the edge of the ball striking face 17. In other words, it is surmised that with the perimeter stiffening element, the cylindrical section of the body deforms less aft of the face, because the body is somewhat isolated from the face in terms of deformations. Additionally, the peak radial deformations occur earlier during the impact time (0.00021 seconds with the presence of the perimeter stiffening element (FIG. 10), rather than 0.00025 seconds without the presence of the perimeter stiffening element (FIG. 9)). The dynamic nodal analyses shows that the combination of these factors allows the club head 14 to return more energy to the golf ball, rather than dissipating it through vibrations in the rest of the club head 14 (e.g., in the frame member, in the crown 18, in the sole 28, etc.). Thus, a significant increase in COR may be produced.

Without the perimeter stiffening element 117, the ball striking surface 17 may flex more than it would with the perimeter stiffening element 117 present, which may result in greater stress and/or deformation of the material of the ball striking surface 17 and thus increased likelihood of cracking, fatigue, strain failure, etc. Further, without the perimeter stiffening element 117, the thin-walled frame member 19 may flex more than it would with the addition of the perimeter stiffening element 117, which may result in greater stress and/or deformation of the material of the frame member 19 and the corresponding increased likelihood of cracking, fatigue, strain failure, etc. Thus, for both these reasons, the inclusion of the perimeter stiffening element 117 in the front body portion 14 a may allow a club head designer to maintain the COR response of the club head within USGA limits while preventing or greatly inhibiting detrimental overflexing of the ball striking surface 17 and/or the thin-walled frame member 19.

According to some aspects, the perimeter stiffening element 117 may have a varying flexibility or stiffness along portions of the perimeter 17 d of the ball striking face 17. The stiffness may vary due to varying a bending stiffness EI_(B) of the perimeter stiffening element 117 and/or varying a torsional stiffness GJ of the perimeter stiffening element 117. For purposes of this disclosure, E refers to Young's modulus (i.e., a material property related to the elastic stress-strain deformation of the material), I_(B) refers to a bending moment of inertia (i.e., a property of the cross-section related to out-of-plane bending of the perimeter stiffness element relative to its midplane), G refers to a modulus of rigidity of the material (i.e., a shear modulus), and J refers to a torsional or polar moment of inertia (i.e., a property of the cross-section related to twisting of the perimeter stiffening element relative to its central axis). By way of non-limiting examples, the bending stiffness EI_(B) may range from 500 in²-lb to 5000 in²-lb, from 1000 in²-lb to 3000 in²-lb, or even from 1500 in²-lb to 2500 in²-lb. Further, by way of non-limiting examples, the torsional stiffness GJ may range from 100 in²-lb to 3000 in²-lb, 500 in²-lb to 2000 in²-lb, or even from 1200 in²-lb to 1600 in²-lb. Thus, it is understood, given the benefit of the present disclosure, that the bending and/or torsional stiffness of the perimeter stiffening element 117 may be optimized by a golf club designer to achieve the desired COR while avoiding detrimental stresses and/or strains in the ball striking face 17 and/or in the frame member 19.

FIGS. 11A-11D illustrate, by way of non-limiting examples, various alternate arrangements of the perimeter stiffening element 117 according to aspects described herein. FIG. 11A illustrates one example, wherein the perimeter stiffening element 117 has a cross-section that is essentially shaped as a parallelogram having a thickness t₃ that is approximately equal to its width w₃. In FIG. 11B the perimeter stiffening element 117 has a cross-section that is essentially shaped as a triangle. For this configuration, the thickness t₃ of the perimeter stiffening element 117 is measured where the thickness dimension of the particular cross-section of the perimeter stiffening element 117 is a maximum. Similarly, the width w₃ of the perimeter stiffening element 117 is measured where the width dimension of the particular cross-section of the perimeter stiffening element 117 is a maximum. FIG. 11C illustrates a perimeter stiffening element 117 having a cross-section with a concave surface feature. FIG. 11D illustrates a perimeter stiffening element 117 having a cross-section with a convexly curved surface. As with the triangular shaped perimeter stiffening element 117 of FIG. 11B, the thickness t₃ of the perimeter stiffening element 117 is measured at its maximum, and the width w₃ of the perimeter stiffening element 117 is also measured at its maximum. Optionally, the perimeter stiffening element 117 need not be nestled all the way into the interior corner formed by the intersection of the ball striking face 17 and the frame member 19. This option is shown in FIG. 11D, wherein the inner surface of the perimeter stiffening element 117 has been formed as a concave groove. Given the benefit of this disclosure, it is understood that the perimeter stiffening element 117 may assume other cross-section shapes (e.g., channels, hollow elements, angles, etc.).

Referring back to FIG. 8, the perimeter stiffening element 117 may extend completely and/or continuously around the perimeter 17 d of the ball striking face. According to other aspects, however, the perimeter stiffening element 117 need not extend completely and/or continuously around the perimeter 17 d of the ball striking face 17. For example, the perimeter stiffening element 117 may extend only partially along the perimeter 17 d of the ball striking face 17. Thus, according one embodiment as shown in FIG. 12, the perimeter stiffening element 17 may extend along a majority of the perimeter 17 d of the ball striking face 17. In FIG. 12, the perimeter stiffening element 117 a is shown extending adjacent to and continuously along the crown 18 and the perimeter stiffening element 117 b is shown extending adjacent to and continuously along the sole 28. In this example, the perimeter stiffening element(s) do not extend across the toe 20 and/or across the heel 24. In other words, there may be one or more segments along the perimeter 17 d that do not include a perimeter stiffener element 117. Optionally, perimeter stiffening elements 117 having different stiffness characteristics (e.g., t₃, w₃, A, EI_(B), GJ) may be provided along different portions of the perimeter 17 d. Thus, by way of non-limiting example, a first perimeter stiffening element 117 a having a first set of stiffness characteristics may be included along at least a portion of the crown 18 and a second perimeter stiffening element 117 b having a second, different set of stiffness characteristics may be included along at least a portion of the sole 28.

According to certain aspects, the front body portion 14 a, which includes the ball striking face 17, the frame member 19 and the perimeter stiffness element 117, may be formed from a single piece of material. For example, the front body portion 14 a may be formed of a metal material, such as a titanium alloy (e.g., Ti-6Al-4V). Other high strength materials, such as stainless steel or amorphous metallic alloys, may be used. The front body portion 14 a may be forged, drawn, cast, machined, injection molded, powder-metal formed, milled, etched, etc. Thus, by way of non-limiting example, the front body portion 14 a may be unitarily formed as a cup face structure. Alternatively, the front body portion 14 a may be formed from multiple pieces of material that are subsequently integrally joined. Thus, by way of another non-limiting example, the ball striking face 17 and the frame member 19 may be unitarily formed as a separate piece and the perimeter stiffness element 117 may be formed as a separate piece or pieces of material that are subsequently integrally joined to ball striking face 17 and to the frame member 19 such as by welding, brazing, cementing, adhesively joining, etc.

Still further, the perimeter stiffening element 117 may be formed in a variety of different ways. According to certain aspects, the perimeter stiffening element 117 may be unitarily constructed with the ball striking face 17, such as by cutting, milling, forging, or other such technique. It is understood that the perimeter stiffening element 117 may be unitarily constructed with the ball striking face 17 and then subsequently shaped or finished with secondary machining operations, such as milling, grinding, etc. In other embodiments, for example, in the case of a multi-piece ball striking face 17, the perimeter stiffening element 117 may be formed separately and subsequently integrally joined with the ball striking face 17. Again, secondary machining operations may be used to shape or refine the ball striking face 17 and/or the perimeter stiffening element 117.

Optionally, the perimeter stiffness element 117 may formed from multiple pieces. For example, as shown in FIG. 12, perimeter stiffening element 117 may be formed as two or more separate perimeter elements, e.g., elements 117 a and 117 b. Alternatively, the perimeter stiffening element 117 may be formed of two or more aligned and overlapping elements or partially aligned and/or overlapping elements. For example, as shown in FIG. 13, a first perimeter element 117 c having a first width w₃′ may extend continuously around the perimeter 17 d of the ball striking surface 17 and a second perimeter element 117 d having a second width w₃″ may lie on top of first perimeter element 117 c. The second perimeter element 117 d is shown extending circumferentially and continuously over the top surface of first perimeter element 117 c. In the general case, neither the first perimeter element 117 c nor second perimeter element 117 d need extend around the entire perimeter 17 d of the ball striking face 17. The perimeter stiffening element 117 may be formed by the first and second perimeter elements 117 c and 117 d continuously or discontinuously joined to one another, for example by bonding, welding, brazing, mechanically fastening, and other joining techniques known to persons of ordinary skill in the art. Thus, it is to be understood that the perimeter stiffening element 117 may be formed using any suitable technique.

The perimeter stiffening element 117 may be formed of any suitable material, including metals, non-metals and composites. For example, the perimeter stiffening element 117 may be formed of a lightweight material, such as a lightweight metal. Some example lightweight metals that may be used include steel, titanium and titanium alloys, aluminum and aluminum alloys, magnesium and magnesium alloys, etc. Additionally or alternatively, the perimeter stiffening element 117 may be formed, at least in part, of non-metallic materials, including composite materials, such as carbon fiber composite materials, fiberglass composite materials, basalt fiber composite materials, polymer materials, ceramics, etc. Even further, the perimeter stiffening element 117 may be formed of more than one material.

According to other aspects, the club head 14 may be provided with other features. For example, referring back to FIGS. 1-8, the club head 14 may have a smooth, convexly-curved crown 18. The club head 14 may additionally have a smooth, convexly-curved sole 28. The curvature of the crown 18 and/or the sole 28 may be uninterrupted from front-to-back and/or heel-to-toe. Further, referring in particular to FIG. 7, the curvature of the crown 18 and/or the sole 28 may be very shallow, especially in the front-to back direction in the forward part of the club head 14. Even further, the overall curvature of the crown 18 in the front-to-back direction may be greater than the overall curvature of the sole 28 in the front-to-back direction.

As another example feature, the club head 14 may include a groove 29 formed about a portion of a periphery of the club head 14. Groove 29 may function as a Kammback feature during at least certain portions of the downswing of the golf club 10. As illustrated in FIGS. 3-6, groove 29 extends along a portion of toe 20 in a generally front-to-back direction, continues onto the rear 22 and extends completely along the rear 22 in a generally heel-to-toe direction, and continues onto the heel 24 and extends along at a portion of heel 24 in a generally front-to-back direction. As can be seen in FIGS. 3 and 5, groove 29 has a tapered ends, with the end of the groove 29 in the heel 24 (FIG. 5) being tapered slightly more than the end of the groove 29 in the toe 20 (FIG. 3). It is to be understood that groove 29 may be discontinuous. Further, it is to be understood that groove 29 may extend only along at least a portion the rear 22, or only along at least a portion of the toe, or only along a portion of the heel 24. In the illustrated embodiment, groove 29 is substantially U-shaped. Further, in the illustrated embodiment, the depth of the groove 29 is less than the height of the groove 29. It is to be understood that other groove shapes may be adopted.

Generally, golf club heads may generally include a plurality of different regions, segments, portions, ends, etc. In an example embodiment, a golf club head may generally include a ball striking face, a rear, a toe, a heel, a crown, a sole and/or a hosel region that may, taken together, generally, enclose an interior of the golf club head. The golf club heads may include a multiple piece construction and structure, or if desired, various portions of the club head structure may be integrally formed with one another, as a unitary, one piece construction. Optionally, the various portions of the club head structure (such as the sole, the crown, the face, the rear, etc.) individually may be formed from multiple pieces of material and subsequently joined using integral joining techniques (e.g., thereby forming an integrally joined crown, an integrally joined sole, an integrally joined aft body portion, etc.) without departing from this invention. Also, as other alternative, if desired, a one piece, unitarily constructed front body portion may be attached to a one piece, unitarily constructed club head aft body portion (optionally, a hollow body, etc.). As even another alternative, the entire club head may be made or formed as a single, one piece, unitary construction.

III. CONCLUSION

As mentioned above, aspects of the invention described herein may be used with various other types of golf clubs and golf club head structures, including hybrid type clubs, iron-type clubs, and the like. Although the above description of golf club structures is generally directed to wood-type golf club heads, nothing in the disclosure should be viewed as limiting use of the invention as described herein to use with only wood-type golf clubs.

The present invention is described above and in the accompanying drawings with reference to a variety of example structures, features, elements, and combinations of structures, features, and elements. The purpose served by the disclosure, however, is to provide examples of the various features and concepts related to the invention, not to limit the scope of the invention. One skilled in the relevant art will recognize that numerous variations and modifications may be made to the embodiments described above without departing from the scope of the present invention, as defined by the appended claims. For example, the various features and concepts described above may be used individually and/or in any combination or subcombination without departing from this invention. 

What is claimed is:
 1. A wood-type golf club head, comprising: a ball striking face; a frame member extending rearwardly from a perimeter of the ball striking face; and a perimeter stiffening element extending along at least a portion of the perimeter of the ball striking face and extending from the ball striking face to the frame member, wherein the thickness of the ball striking face is less than or equal to 2.0 mm, and wherein the cross-sectional area of the perimeter stiffening element is greater than or equal to 10 mm².
 2. The golf club head of claim 1, wherein the thickness of the frame member is less than or equal to 1.0 mm.
 3. The golf club head of claim 1, wherein the out-of-plane bending stiffness (EI_(B)) of the perimeter stiffening element ranges from 1500 in²-lb to 2500 in²-lb.
 4. The golf club head of claim 1, wherein the torsional stiffness (GJ) of the perimeter stiffening element ranges from 1200 in²-lb to 1600 in²-lb.
 5. The golf club head of claim 1, wherein the coefficient of restitution of the club head is greater than or equal to 0.830.
 6. The golf club head of claim 1, wherein the thickness of the perimeter stiffening element is greater than or equal to 4.0 mm and the width of the perimeter stiffening element is greater than or equal to 3.0 mm.
 7. The golf club head of claim 1, wherein the cross-sectional area of the perimeter stiffening element is greater than or equal to 15 mm².
 8. The golf club head of claim 1, wherein the ball striking face, the frame member and the perimeter stiffening element are unitarily formed.
 9. The golf club head of claim 1, wherein the ball striking face, the frame member and the perimeter stiffening element are formed of a titanium material.
 10. The golf club head of claim 1, wherein the ratio of the thickness of the ball striking face adjacent to the perimeter stiffening element to the thickness of the frame member adjacent to the perimeter stiffening element is greater than or equal to approximately 1.5:1.
 11. The golf club head of claim 1, wherein the thickness of the ball striking face adjacent to the perimeter stiffening element ranges from approximately 0.5 mm to approximately 2.5 mm.
 12. The golf club head of claim 1, wherein the thickness of the frame member adjacent to the perimeter stiffening element ranges from approximately 0.25 mm to approximately 1.25 mm.
 13. The golf club head of claim 1, wherein the ratio of the thickness of the perimeter stiffening element to the width to the perimeter stiffening element is greater than or equal to 1:1.
 14. The golf club head of claim 1, wherein the ratio of the thickness of the perimeter stiffening element to the thickness of the ball striking face adjacent to the perimeter stiffening element ranges from approximately 2:1 to approximately 4:1.
 15. The golf club head of claim 1, wherein the thickness of the perimeter stiffening element ranges from approximately 2.5 mm to approximately 7.5 mm.
 16. The golf club head of claim 1, wherein the width of the perimeter stiffening element has a value that is within ±20% of the value of the thickness of the perimeter stiffening element.
 17. The golf club head of claim 1, wherein the perimeter stiffening element is integrally joined to the frame member.
 18. The golf club head of claim 1, wherein the perimeter stiffening element is integrally joined to the ball striking face.
 19. The golf club head of claim 1, wherein the club head has an interior cavity.
 20. The golf club head of claim 1, wherein the club head has a volume greater than or equal to 440 cc.
 21. The golf club head of claim 1, wherein the ball striking face has an area greater than or equal to 32 cm².
 22. A golf club comprising: a wood-type golf club head having: a ball striking face; a frame member extending rearwardly from a perimeter of the ball striking face; and a perimeter stiffening element extending along at least a portion of the perimeter of the ball striking face and extending from the ball striking face to the frame member, wherein the thickness of the ball striking face is less than or equal to 2.0 mm, and wherein the cross-sectional area of the perimeter stiffening element is greater than or equal to 10 mm²; and a shaft attached to the golf club head.
 23. A golf club head, comprising: a ball striking face configured to flex inward upon contacting a golf ball; a frame member extending around and integrally joined to the ball striking face; and a perimeter stiffening element extending around at least majority of a perimeter of the ball striking face, the perimeter stiffening element being integrally joined to an interior surface of the ball striking face and to an interior surface of the frame member, wherein the ball striking face has a thickness adjacent to the perimeter stiffening element that ranges from approximately 1.25 mm to approximately 2.5 mm, and wherein the frame member has a thickness adjacent to the perimeter stiffening element that ranges from approximately 0.40 mm to approximately 1.0 mm, wherein the perimeter stiffening element has a cross-sectional area greater than or equal to 20 mm², and wherein the coefficient of restitution of the club head is greater than or equal to 0.830.
 24. A wood-type golf club head having a volume greater than or equal to 440 cc and a ball striking face area greater than or equal to 32 cm², the golf club head comprising: a ball striking face; a frame member extending rearwardly from a perimeter of the ball striking face; and a perimeter stiffening element located along at least a majority of the perimeter of the ball striking face, the perimeter stiffening element extending from the ball striking face to the frame member, wherein a thickness of the perimeter stiffening element is greater than or equal to a thickness of the ball striking face adjacent to the perimeter stiffening element, and wherein a width of the perimeter stiffening element is greater than or equal to a thickness of the frame element adjacent to the perimeter stiffening element.
 25. The golf club head of claim 24, wherein the thickness of the perimeter stiffening element is greater than one-and-a-half times the thickness of the ball striking face.
 26. The golf club head of claim 24, wherein the thickness of the perimeter stiffening element is greater than twice the thickness of the ball striking face.
 27. The golf club head of claim 24, wherein the width of the perimeter stiffening element is greater than twice the thickness of the frame element.
 28. The golf club head of claim 24, wherein the width of the perimeter stiffening element is greater than triple the thickness of the frame element.
 29. The golf club head of claim 24, wherein the thickness of the perimeter stiffening element is greater than or equal to the width of the perimeter stiffening element.
 30. The golf club head of claim 24, wherein the thickness of the ball striking face adjacent to the perimeter stiffening element is greater than the thickness of the frame member adjacent to the perimeter stiffening element.
 31. The golf club head of claim 24, wherein the coefficient of restitution of the club head is greater than or equal to 0.830. 